docs: def _handle_relation(self, tokens: ParseResults) -> str:
          """Handle a relation."""
          subject_node_dsl = self.ensure_node(tokens[SUBJECT])
          object_node_dsl = self.ensure_node(tokens[OBJECT])
  
          subject_modifier = modifier_po_to_dict(tokens[SUBJECT])
          object_modifier = modifier_po_to_dict(tokens[OBJECT])
  
          annotations = {
              annotation_name: (
                  {
                      ae: True
                      for ae in annotation_entry
                  }
                  if isinstance(annotation_entry, set) else
                  {
                      annotation_entry: True
                  }
              )
              for annotation_name, annotation_entry in self.control_parser.annotations.items()
          }
  
          return self._add_qualified_edge(
              subject_node_dsl,
              object_node_dsl,
              relation=tokens[RELATION],
              annotations=annotations,
              subject_modifier=subject_modifier,
              object_modifier=object_modifier,
          )